........... Typing "helpusobi1" or "devmapall" and then typing "playermodel maul" doesn't work for me.

I think you are confused between "modeling" and "skinning." What do you want?
(1) A model is the base of any character in the game.
(2) A skin is the texture on that model. You can have the same model and different skins to make different characters.

There is a lot of posts in the forums about putting a new player models in SP. Why don't you try looking them up. It's already been addressed.